.\" ----------------------------------------------------------------------------
.\" Make sure there are no errors with:
.\" groff -z -wall -b -e -t multipath/multipath.conf.5
.\" man --warnings -E UTF-8 -l -Tutf8 -Z multipath/multipath.conf.5 >/dev/null
.\"
.\" Update the date below if you make any significant change.
.\" ----------------------------------------------------------------------------
.
.TH MULTIPATH.CONF 5 2021-09-08 Linux
.
.
.\" ----------------------------------------------------------------------------
.SH NAME
.\" ----------------------------------------------------------------------------
.
multipath.conf \- multipath daemon configuration file.
.
.
.\" ----------------------------------------------------------------------------
.SH DESCRIPTION
.\" ----------------------------------------------------------------------------
.
.B "/etc/multipath.conf"
is the configuration file for the multipath daemon. It is used to
overwrite the built-in configuration table of \fBmultipathd\fP.
Any line whose first non-white-space character is a '#' is considered
a comment line. Empty lines are ignored.
.PP
Currently used multipathd configuration can be displayed with the \fBmultipath -t\fR
or \fBmultipathd show config\fR command.
.
.
.\" ----------------------------------------------------------------------------
.SH SYNTAX
.\" ----------------------------------------------------------------------------
.
The configuration file contains entries of the form:
.RS
.nf
.ft B
.sp
<section> {
.RS
.ft B
<attribute> <value>
.I "..."
.ft B
<subsection> {
.RS
.ft B
<attribute> <value>
.I "..."
.RE
.ft B
}
.RE
.ft B
}
.ft R
.fi
.RE
.LP
Each \fIsection\fP contains one or more attributes or subsections. The
recognized keywords for attributes or subsections depend on the
section in which they occur.
.LP
.
\fB<attribute>\fR and \fB<value>\fR must be on a single line.
\fB<attribute>\fR is one of the keywords listed in this man page.
\fB<value>\fR is either a simple word (containing no whitespace and none of the
characters '\(dq', '#', and '!') or \fIone\fR string enclosed in double
quotes ("..."). Outside a quoted string, text starting with '#', and '!' is
regarded as a comment and ignored until the end of the line. Inside a quoted
string, '#' and '!' are normal characters, and whitespace is preserved.
To represent a double quote character inside a double quoted string, use two
consecutive double quotes ('""'). Thus '2.5\(dq SSD' can be written as "2.5"" SSD".
.LP
.
Opening braces ('{') must follow the (sub)section name on the same line. Closing
braces ('}') that mark the end of a (sub)section must be the only non-whitespace
character on the line. Whitespace is ignored except inside double quotes, thus
the indentation shown in the above example is helpful for human readers but
not mandatory.
.LP
.
.LP
.B Note on regular expressions:
The \fImultipath.conf\fR syntax allows many attribute values to be specified as POSIX
Extended Regular Expressions (see \fBregex\fR(7)). These regular expressions
are \fBcase sensitive\fR and \fBnot anchored\fR, thus the expression "bar" matches "barbie",
"rhabarber", and "wunderbar", but not "Barbie". To avoid unwanted substring
matches, standard regular expression syntax using the special characters "^" and "$" can be used.
.
.LP
.
The following \fIsection\fP keywords are recognized:
.TP 17
.B defaults
This section defines default values for attributes which are used
whenever no values are given in the appropriate device or multipath
sections.
.TP
.B blacklist
This section defines which devices should be excluded from the
multipath topology discovery.
.TP
.B blacklist_exceptions
This section defines which devices should be included in the
multipath topology discovery, despite being listed in the
\fIblacklist\fR section.
.TP
.B multipaths
This section defines the multipath topologies. They are indexed by a
\fIWorld Wide Identifier\fR(WWID). For details on the WWID generation
see section \fIWWID generation\fR below. Attributes set in this section take
precedence over all others.
.TP
.B devices
This section defines the device-specific settings. Devices are identified by
vendor, product, and revision.
.TP
.B overrides
This section defines values for attributes that should override the
device-specific settings for all devices.
.RE
.LP
.
.
.\" ----------------------------------------------------------------------------
.SH "defaults section"
.\" ----------------------------------------------------------------------------
.
The \fIdefaults\fR section recognizes the following keywords:
.
.
.TP 17
.B verbosity
Default verbosity. Higher values increase the verbosity level. Valid
levels are between 0 and 6.
.RS
.TP
The default is: \fB2\fR
.RE
.
.
.TP
.B polling_interval
Interval between two path checks in seconds. For properly functioning paths,
the interval between checks will gradually increase to \fImax_polling_interval\fR.
This value will be overridden by the \fIWatchdogSec\fR
setting in the multipathd.service definition if systemd is used.
.RS
.TP
The default is: \fB5\fR
.RE
.
.
.TP
.B max_polling_interval
Maximal interval between two path checks in seconds.
.RS
.TP
The default is: \fB4 * polling_interval\fR
.RE
.
.
.TP
.B reassign_maps
Enable reassigning of device-mapper maps. With this option multipathd
will remap existing device-mapper maps to always point to multipath
device, not the underlying block devices. Possible values are
\fIyes\fR and \fIno\fR.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B multipath_dir
This option is deprecated, and will be removed in a future release.
Directory where the dynamic shared objects are stored. Defined at compile time,
commonly \fI/lib64/multipath/\fR or \fI/lib/multipath/\fR.
.RS
.TP
The default is: \fB<system dependent>\fR
.RE
.
.
.TP
.B path_selector
The default path selector algorithm to use; they are offered by the
kernel multipath target:
.RS
.TP 12
.I "round-robin 0"
Loop through every path in the path group, sending the same amount of I/O to
each. Some aspects of behavior can be controlled with the attributes:
\fIrr_min_io\fR, \fIrr_min_io_rq\fR and \fIrr_weight\fR.
.TP
.I "queue-length 0"
(Since 2.6.31 kernel) Choose the path for the next bunch of I/O based on the amount
of outstanding I/O to the path.
.TP
.I "service-time 0"
(Since 2.6.31 kernel) Choose the path for the next bunch of I/O based on the amount
of outstanding I/O to the path and its relative throughput.
.TP
.I "historical-service-time 0"
(Since 5.8 kernel) Choose the path for the next bunch of I/O based on the
estimation of future service time based on the history of previous I/O submitted
to each path.
.TP
.I "io-affinity 0"
(Since 5.11 kernel) Choose the path for the next bunch of I/O based on a CPU to
path mapping the user passes in and what CPU we are executing on.
.TP
The default is: \fBservice-time 0\fR
.RE
.
.
.TP
.B path_grouping_policy
The default path grouping policy to apply to unspecified
multipaths. Possible values are:
.RS
.TP 12
.I failover
One path per priority group.
.TP
.I multibus
All paths in one priority group.
.TP
.I group_by_serial
One priority group per serial number.
.TP
.I group_by_prio
One priority group per priority value. Priorities are determined by
callout programs specified as a global, per-controller or
per-multipath option in the configuration file.
.TP
.I group_by_node_name
One priority group per target node name. Target node names are fetched
in \fI/sys/class/fc_transport/target*/node_name\fR.
.TP
The default is: \fBfailover\fR
.RE
.
.
.TP
.B uid_attrs
.
Setting this option activates \fBmerging uevents\fR by WWID, which may improve
uevent processing effiency. Moreover, it's an alternative method to configure
the udev properties to use for determining unique path identifiers (WWIDs).
.RS
.PP
The value of this option is a space separated list of records like
\(dq\fItype:ATTR\fR\(dq, where \fItype\fR is matched against the beginning
of the device node name (e.g. \fIsd:ATTR\fR matches \fIsda\fR), and
\fIATTR\fR is the name of the udev property to use for matching devices.
.PP
If this option is configured and matches the device
node name of a device, it overrides any other configured  methods for
determining the WWID for this device.
.PP
The default is: \fB<unset>\fR. To enable uevent merging, set it e.g. to
\(dqsd:ID_SERIAL dasd:ID_UID nvme:ID_WWN\(dq.
.RE
.
.
.TP
.B uid_attribute
The udev attribute providing a unique path identifier (WWID). If
\fIuid_attribute\fR is set to the empty string, WWID determination is done
using the \fIsysfs\fR method rather then using udev (not recommended in
production; see \fBWWID generation\fR below).
.RS
.TP
The default is: \fBID_SERIAL\fR, for SCSI devices
.TP
The default is: \fBID_UID\fR, for DASD devices
.TP
The default is: \fBID_WWN\fR, for NVMe devices
.RE
.
.
.TP
.B getuid_callout
(Superseded by \fIuid_attribute\fR) The default program and args to callout
to obtain a unique path identifier. Should be specified with an absolute path.
.RS
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B prio
The name of the path priority routine. The specified routine
should return a numeric value specifying the relative priority
of this path. Higher number have a higher priority.
\fI"none"\fR is a valid value. Currently the following path priority routines
are implemented:
.RS
.TP 12
.I const
Return a constant priority of \fI1\fR.
.TP
.I sysfs
Use the sysfs attributes \fIaccess_state\fR and \fIpreferred_path\fR to
generate the path priority. This prioritizer accepts the optional prio_arg
\fIexclusive_pref_bit\fR.
.TP
.I emc
(Hardware-dependent)
Generate the path priority for DGC class arrays as CLARiiON CX/AX and
EMC VNX and Unity families.
.TP
.I alua
(Hardware-dependent)
Generate the path priority based on the SCSI-3 ALUA settings. This prioritizer
accepts the optional prio_arg \fIexclusive_pref_bit\fR.
.TP
.I ontap
(Hardware-dependent)
Generate the path priority for NetApp ONTAP class and OEM arrays as IBM NSeries.
.TP
.I rdac
(Hardware-dependent)
Generate the path priority for LSI/Engenio/NetApp RDAC class as NetApp SANtricity
E/EF Series, and OEM arrays from IBM DELL SGI STK and SUN.
.TP
.I hp_sw
(Hardware-dependent)
Generate the path priority for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with
Active/Standby mode exclusively.
.TP
.I hds
(Hardware-dependent)
Generate the path priority for Hitachi AMS families of arrays other than AMS 2000.
.TP
.I random
Generate a random priority between 1 and 10.
.TP
.I weightedpath
Generate the path priority based on the regular expression and the
priority provided as argument. Requires prio_args keyword.
.TP
.I path_latency
Generate the path priority based on a latency algorithm.
Requires prio_args keyword.
.TP
.I ana
(Hardware-dependent)
Generate the path priority based on the NVMe ANA settings.
.TP
.I datacore
(Hardware-dependent)
Generate the path priority for some DataCore storage arrays. Requires prio_args
keyword.
.TP
.I iet
(iSCSI only)
Generate path priority for iSCSI targets based on IP address. Requires
prio_args keyword.
.PP
The default depends on the \fBdetect_prio\fR setting: If \fBdetect_prio\fR is
\fByes\fR (default), the default priority algorithm is \fBsysfs\fR (except for
NetAPP E-Series, where it is \fBalua\fR). If \fBdetect_prio\fR is
\fBno\fR, the default priority algorithm is \fBconst\fR.
.RE
.
.
.TP
.B prio_args
Arguments to pass to to the prio function. This only applies to certain
prioritizers:
.RS
.TP 12
.I weighted
Needs a value of the form
\fI"<hbtl|devname|serial|wwn> <regex1> <prio1> <regex2> <prio2> ..."\fR
.RS
.TP 8
.I hbtl
Regex can be of SCSI H:B:T:L format. For example: 1:0:.:. , *:0:0:.
.TP
.I devname
Regex can be of device name format. For example: sda , sd.e
.TP
.I serial
Regex can be of serial number format. For example: .*J1FR.*324 . The serial can
be looked up through sysfs or by running multipathd show paths format "%z". For
example: 0395J1FR904324
.TP
.I wwn
Regex can be of the form \fI"host_wwnn:host_wwpn:target_wwnn:target_wwpn"\fR
these values can be looked up through sysfs or by running \fImultipathd show paths format
"%N:%R:%n:%r"\fR. For example: 0x200100e08ba0aea0:0x210100e08ba0aea0:.*:.* , .*:.*:iqn.2009-10.com.redhat.msp.lab.ask-06:.*
.RE
.TP 12
.I path_latency
Needs a value of the form "io_num=\fI<20>\fR base_num=\fI<10>\fR"
.RS
.TP 8
.I io_num
The number of read IOs sent to the current path continuously, used to calculate the average path latency.
Valid Values: Integer, [2, 200].
.TP
.I base_num
The base number value of logarithmic scale, used to partition different priority ranks. Valid Values: Integer,
[2, 10]. And Max average latency value is 100s, min average latency value is 1us.
For example: If base_num=10, the paths will be grouped in priority groups with path latency <=1us, (1us, 10us],
(10us, 100us], (100us, 1ms], (1ms, 10ms], (10ms, 100ms], (100ms, 1s], (1s, 10s], (10s, 100s], >100s.
.RE
.TP 12
.I alua
If \fIexclusive_pref_bit\fR is set, paths with the \fIpreferred path\fR bit
set will always be in their own path group.
.TP
.I sysfs
If \fIexclusive_pref_bit\fR is set, paths with the \fIpreferred path\fR bit
set will always be in their own path group.
.TP
.I datacore
.RS
.TP 8
.I preferredsds
(Mandatory) The preferred "SDS name".
.TP
.I timeout
(Optional) The timeout for the INQUIRY, in ms.
.RE
.TP 12
.I iet
.RS
.TP 8
.I preferredip=...
(Mandatory) Th preferred IP address, in dotted decimal notation, for iSCSI targets.
.RE
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B features
Specify any device-mapper features to be used. Syntax is \fInum list\fR
where \fInum\fR is the number, between 0 and 8, of features in \fIlist\fR.
Possible values for the feature list are:
.RS
.TP 12
.I queue_if_no_path
(Deprecated, superseded by \fIno_path_retry\fR) Queue I/O if no path is active.
Identical to the \fIno_path_retry\fR with \fIqueue\fR value. If both this
feature and \fIno_path_retry\fR are set, the latter value takes
precedence. See KNOWN ISSUES.
.TP
.I pg_init_retries <times>
(Since kernel 2.6.24) Number of times to retry pg_init, it must be between 1 and 50.
.TP
.I pg_init_delay_msecs <msecs>
(Since kernel 2.6.38) Number of msecs before pg_init retry, it must be between 0 and 60000.
.TP
.I queue_mode <mode>
(Since kernel 4.8) Select the the queueing mode per multipath device.
<mode> can be \fIbio\fR, \fIrq\fR or \fImq\fR, which corresponds to
bio-based, request-based, and block-multiqueue (blk-mq) request-based,
respectively.
The default depends on the kernel parameter \fBdm_mod.use_blk_mq\fR. It is
\fImq\fR if the latter is set, and \fIrq\fR otherwise.
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B path_checker
The default method used to determine the path's state. The synchronous
checkers (all except \fItur\fR and \fIdirectio\fR) will cause multipathd to
pause most activity, waiting up to \fIchecker_timeout\fR seconds for the path
to respond. The asynchronous checkers (\fItur\fR and \fIdirectio\fR) will not
pause multipathd. Instead, multipathd will check for a response once per
second, until \fIchecker_timeout\fR seconds have elapsed. Possible values are:
.RS
.TP 12
.I readsector0
(Deprecated) Read the first sector of the device. This checker is being
deprecated, please use \fItur\fR instead.
.TP
.I tur
Issue a \fITEST UNIT READY\fR command to the device.
.TP
.I emc_clariion
(Hardware-dependent)
Query the DGC/EMC specific EVPD page 0xC0 to determine the path state
for CLARiiON CX/AX and EMC VNX and Unity arrays families.
.TP
.I hp_sw
(Hardware-dependent)
Check the path state for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with
Active/Standby mode exclusively.
.TP
.I rdac
(Hardware-dependent)
Check the path state for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF
Series, and OEM arrays from IBM DELL SGI STK and SUN.
.TP
.I directio
Read the first sector with direct I/O. This checker could cause spurious path
failures under high load. Increasing \fIchecker_timeout\fR can help with this.
.TP
.I cciss_tur
(Hardware-dependent)
Check the path state for HP/COMPAQ Smart Array(CCISS) controllers.
.TP
.I none
Do not check the device, fallback to use the values retrieved from sysfs
.TP
The default is: \fBtur\fR
.RE
.
.
.TP
.B alias_prefix
The \fIuser_friendly_names\fR prefix.
.RS
.TP
The default is: \fBmpath\fR
.RE
.
.
.TP
.B failback
Tell multipathd how to manage path group failback.
To select \fIimmediate\fR or a \fIvalue\fR, it's mandatory that the device
has support for a working prioritizer.
.RS
.TP 12
.I immediate
Immediately failback to the highest priority pathgroup that contains
active paths.
.TP
.I manual
Do not perform automatic failback.
.TP
.I followover
Used to deal with multiple computers accessing the same Active/Passive storage
devices. Only perform automatic failback when the first path of a pathgroup
becomes active. This keeps a cluster node from automatically failing back when
another node requested the failover.
.TP
.I values > 0
Deferred failback (time to defer in seconds).
.TP
The default is: \fBmanual\fR
.RE
.
.
.TP
.B  rr_min_io
Number of I/O requests to route to a path before switching to the next in the
same path group. This is only for \fIBlock I/O\fR(BIO) based multipath and
only apply to \fIround-robin\fR path_selector.
.RS
.TP
The default is: \fB1000\fR
.RE
.
.
.TP
.B rr_min_io_rq
Number of I/O requests to route to a path before switching to the next in the
same path group. This is only for \fIRequest\fR based multipath and
only apply to \fIround-robin\fR path_selector.
.RS
.TP
The default is: \fB1\fR
.RE
.
.
.TP
.B max_fds
Specify the maximum number of file descriptors that can be opened by multipath
and multipathd. This is equivalent to ulimit \-n. A value of \fImax\fR will set
this to the system limit from \fI/proc/sys/fs/nr_open\fR. If this is not set, the
maximum number of open fds is taken from the calling process. It is usually
1024. To be safe, this should be set to the maximum number of paths plus 32,
if that number is greated than 1024.
.RS
.TP
The default is: \fBmax\fR
.RE
.
.
.TP
.B rr_weight
If set to \fIpriorities\fR the multipath configurator will assign path weights
as "path prio * rr_min_io". Possible values are
.I priorities
or
.I uniform .
Only apply to \fIround-robin\fR path_selector.
.RS
.TP
The default is: \fBuniform\fR
.RE
.
.
.TP
.B no_path_retry
Specify what to do when all paths are down. Possible values are:
.RS
.TP 12
.I value > 0
Number of retries until disable I/O queueing.
.TP
.I fail
For immediate failure (no I/O queueing).
.TP
.I queue
For never stop I/O queueing, similar to \fIqueue_if_no_path\fR. See KNOWN ISSUES.
.TP
The default is: \fBfail\fR
.RE
.
.
.TP
.B queue_without_daemon
If set to
.I no
, when multipathd stops, queueing will be turned off for all devices.
This is useful for devices that set no_path_retry. If a machine is
shut down while all paths to a device are down, it is possible to hang waiting
for I/O to return from the device after multipathd has been stopped. Without
multipathd running, access to the paths cannot be restored, and the kernel
cannot be told to stop queueing I/O. Setting queue_without_daemon to
.I no
, avoids this problem.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B checker_timeout
Specify the timeout to use for path checkers and prioritizers, in seconds.
Only prioritizers that issue scsi commands use checker_timeout.  If a path
does not respond to the checker command after \fIchecker_timeout\fR
seconds have elapsed, it is considered down.
.RS
.TP
The default is: in \fB/sys/block/<dev>/device/timeout\fR
.RE
.
.
.TP
.B allow_usb_devices
If set to
.I no
, all USB devices will be skipped during path discovery. If you intend to use
multipath on USB attached devices, set this to \fIyes\fR.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B flush_on_last_del
If set to
.I yes
, multipathd will disable queueing when the last path to a device has been
deleted.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B user_friendly_names
If set to
.I yes
, using the bindings file \fI/etc/multipath/bindings\fR to assign a persistent
and unique alias to the multipath, in the form of mpath<n>. If set to
.I no
use the WWID as the alias. In either case this be will
be overridden by any specific aliases in the \fImultipaths\fR section.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B fast_io_fail_tmo
Specify the number of seconds the SCSI layer will wait after a problem has been
detected on a FC remote port before failing I/O to devices on that remote port.
This should be smaller than dev_loss_tmo. Setting this to
.I off
will disable the timeout.
.RS
.TP
The default is: \fB5\fR
.RE
.
.
.TP
.B dev_loss_tmo
Specify the number of seconds the SCSI layer will wait after a problem has
been detected on a FC remote port before removing it from the system. This
can be set to "infinity" which sets it to the max value of 2147483647
seconds, or 68 years. It will be automatically adjusted to the overall
retry interval \fIno_path_retry\fR * \fIpolling_interval\fR
if a number of retries is given with \fIno_path_retry\fR and the
overall retry interval is longer than the specified \fIdev_loss_tmo\fR value.
The Linux kernel will cap this value to \fI600\fR if \fIfast_io_fail_tmo\fR
is not set. See KNOWN ISSUES.
.RS
.TP
The default is: \fB600\fR
.RE
.
.
.TP
.B eh_deadline
Specify the maximum number of seconds the SCSI layer will spend doing error
handling when scsi devices fail. After this timeout the scsi layer will perform
a full HBA reset. Setting this may be necessary in cases where the rport is
never lost, so \fIfast_io_fail_tmo\fR and \fIdev_loss_tmo\fR will never
trigger, but (frequently do to load) scsi commands still hang. \fBNote:\fR when
the scsi error handler performs the HBA reset, all target paths on that HBA
will be affected. eh_deadline should only be set in cases where all targets on
the affected HBAs are multipathed.
.RS
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B bindings_file
This option is deprecated, and will be removed in a future release.
The full pathname of the binding file to be used when the user_friendly_names
option is set.
.RS
.TP
The default is: \fB/etc/multipath/bindings\fR
.RE
.
.
.TP
.B wwids_file
This option is deprecated, and will be removed in a future release.
The full pathname of the WWIDs file, which is used by multipath to keep track
of the WWIDs for LUNs it has created multipath devices on in the past.
.RS
.TP
The default is: \fB/etc/multipath/wwids\fR
.RE
.
.
.TP
.B prkeys_file
This option is deprecated, and will be removed in a future release.
The full pathname of the prkeys file, which is used by multipathd to keep
track of the persistent reservation key used for a specific WWID, when
\fIreservation_key\fR is set to \fBfile\fR.
.RS
.TP
The default is: \fB/etc/multipath/prkeys\fR
.RE
.
.
.TP
.B log_checker_err
If set to
.I once
, multipathd logs the first path checker error at logging level 2. Any later
errors are logged at level 3 until the device is restored. If set to
.I always
, multipathd always logs the path checker error at logging level 2.
.RS
.TP
The default is: \fBalways\fR
.RE
.
.
.TP
.B reservation_key
This is the service action reservation key used by mpathpersist. It must be
set for all multipath devices using persistent reservations, and it must be
the same as the RESERVATION KEY field of the PERSISTENT RESERVE OUT parameter
list which contains an 8-byte value provided by the application client to the
device server to identify the I_T nexus. If the \fI--param-aptpl\fR option is
used when registering the key with mpathpersist, \fB:aptpl\fR must be appended
to the end of the reservation key.
.RS
.PP
Alternatively, this can be set to \fBfile\fR, which will store the RESERVATION
KEY registered by mpathpersist in the \fIprkeys_file\fR. multipathd will then
use this key to register additional paths as they appear.  When the
registration is removed, the RESERVATION KEY is removed from the
\fIprkeys_file\fR. The prkeys file will automatically keep track of whether
the key was registered with \fI--param-aptpl\fR.
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B all_tg_pt
Set the 'all targets ports' flag when registering keys with mpathpersist. Some
arrays automatically set and clear registration keys on all target ports from a
host, instead of per target port per host. The ALL_TG_PT flag must be set to
successfully use mpathpersist on these arrays. Setting this option is identical
to calling mpathpersist with \fI--param-alltgpt\fR
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B retain_attached_hw_handler
(Obsolete for kernels >= 4.3) If set to
.I yes
and the SCSI layer has already attached a hardware_handler to the device,
multipath will not force the device to use the hardware_handler specified by
mutipath.conf. If the SCSI layer has not attached a hardware handler,
multipath will continue to use its configured hardware handler.
.RS
.PP
The default is: \fByes\fR
.PP
\fBImportant Note:\fR Linux kernel 4.3 or newer always behaves as if
\fB"retain_attached_hw_handler yes"\fR was set.
.RE
.
.
.TP
.B detect_prio
If set to
.I yes
, multipath will try to detect if the device supports SCSI-3 ALUA. If so, the
device will automatically use the \fIsysfs\fR prioritizer if the required sysf
attributes \fIaccess_state\fR and \fIpreferred_path\fR are supported, or the
\fIalua\fR prioritizer if not. If set to
.I no
, the prioritizer will be selected as usual.
.RS
.TP
The default is: \fByes\fR
.RE
.
.
.TP
.B detect_checker
if set to
.I yes
, multipath will try to detect if the device supports SCSI-3 ALUA. If so, the
device will automatically use the \fItur\fR checker. If set to
.I no
, the checker will be selected as usual.
.RS
.TP
The default is: \fByes\fR
.RE
.
.
.TP
.B force_sync
If set to
.I yes
, multipathd will call the path checkers in sync mode only.  This means that
only one checker will run at a time.  This is useful in the case where many
multipathd checkers running in parallel causes significant CPU pressure.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B strict_timing
If set to
.I yes
, multipathd will start a new path checker loop after exactly one second,
so that each path check will occur at exactly \fIpolling_interval\fR
seconds. On busy systems path checks might take longer than one second;
here the missing ticks will be accounted for on the next round.
A warning will be printed if path checks take longer than \fIpolling_interval\fR
seconds.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B deferred_remove
If set to
.I yes
, multipathd will do a deferred remove instead of a regular remove when the
last path device has been deleted.  This means that if the multipath device is
still in use, it will be freed when the last user closes it.  If path is added
to the multipath device before the last user closes it, the deferred remove
will be canceled.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B partition_delimiter
This parameter controls how multipath chooses the names of partition devices
of multipath maps if a multipath map is renamed (e.g. if a map alias is added
or changed). If this parameter is set to a string other than "/UNSET/" (even
the empty string), multipath inserts that string between device name and
partition number to construct the partition device name.
Otherwise (i.e. if this parameter is unset or has the value "/UNSET/"),
the behavior depends on the map name: if it ends in a digit, a \fI"p"\fR is
inserted between name and partition number; otherwise, the partition number is
simply appended.
Distributions may use a non-null default value for this option; in this case,
the user must set it to "/UNSET/" to obtain the original \fB<unset>\fR
behavior. Use \fImultipath -T\fR to check the current settings.
.RS
.TP
The default is: \fB<unset>\fR
.RE
.
.
.TP
.B config_dir
This option is deprecated, and will be removed in a future release.
If set to anything other than "", multipath will search this directory
alphabetically for file ending in ".conf" and it will read configuration
information from them, just as if it was in \fI/etc/multipath.conf\fR.
config_dir must either be "" or a fully qualified directory name.
.RS
.TP
The default is: \fB/etc/multipath/conf.d/\fR
.RE
.
.
.TP
.B san_path_err_threshold
If set to a value greater than 0, multipathd will watch paths and check how many
times a path has been failed due to errors.If the number of failures on a particular
path is greater then the san_path_err_threshold, then the path will not reinstate
till san_path_err_recovery_time. These path failures should occur within a
san_path_err_forget_rate checks, if not we will consider the path is good enough
to reinstantate. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B san_path_err_forget_rate
If set to a value greater than 0, multipathd will check whether the path failures
has exceeded  the san_path_err_threshold within this many checks i.e
san_path_err_forget_rate . If so we will not reinstante the path till
san_path_err_recovery_time. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B san_path_err_recovery_time
If set to a value greater than 0, multipathd will make sure that when path failures
has exceeded the san_path_err_threshold within san_path_err_forget_rate then the path
will be placed in failed state for san_path_err_recovery_time duration.Once san_path_err_recovery_time
has timeout  we will reinstante the failed path .
san_path_err_recovery_time value should be in secs.
See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B marginal_path_double_failed_time
One of the four parameters of supporting path check based on accounting IO
error such as intermittent error. When a path failed event occurs twice in
\fImarginal_path_double_failed_time\fR seconds due to an IO error and all the
other three parameters are set, multipathd will fail the path and enqueue
this path into a queue of which members are sent a couple of continuous
direct reading asynchronous IOs at a fixed sample rate of 10HZ to start IO
error accounting process. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B marginal_path_err_sample_time
One of the four parameters of supporting path check based on accounting IO
error such as intermittent error. If it is set to a value no less than 120,
when a path fail event occurs twice in \fImarginal_path_double_failed_time\fR
second due to an IO error, multipathd will fail the path and enqueue this
path into a queue of which members are sent a couple of continuous direct
reading asynchronous IOs at a fixed sample rate of 10HZ to start the IO
accounting process for the path will last for
\fImarginal_path_err_sample_time\fR.
If the rate of IO error on a particular path is greater than the
\fImarginal_path_err_rate_threshold\fR, then the path will not reinstate for
\fImarginal_path_err_recheck_gap_time\fR seconds unless there is only one
active path. After \fImarginal_path_err_recheck_gap_time\fR expires, the path
will be requeueed for rechecking. If checking result is good enough, the
path will be reinstated. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B marginal_path_err_rate_threshold
The error rate threshold as a permillage (1/1000). One of the four parameters
of supporting path check based on accounting IO error such as intermittent
error. Refer to \fImarginal_path_err_sample_time\fR. If the rate of IO errors
on a particular path is greater than this parameter, then the path will not
reinstate for \fImarginal_path_err_recheck_gap_time\fR seconds unless there is
only one active path. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B marginal_path_err_recheck_gap_time
One of the four parameters of supporting path check based on accounting IO
error such as intermittent error. Refer to
\fImarginal_path_err_sample_time\fR. If this parameter is set to a positive
value, the failed path of  which the IO error rate is larger than
\fImarginal_path_err_rate_threshold\fR will be kept in failed state for
\fImarginal_path_err_recheck_gap_time\fR seconds. When
\fImarginal_path_err_recheck_gap_time\fR seconds expires, the path will be
requeueed for checking. If checking result is good enough, the path will be
reinstated, or else it will keep failed. See "Shaky paths detection" below.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B delay_watch_checks
This option is \fBdeprecated\fR, and mapped to \fIsan_path_err_forget_rate\fR.
If this is set to a value greater than 0 and no \fIsan_path_err\fR options
are set, \fIsan_path_err_forget_rate\fR will be set to the value of
\fIdelay_watch_checks\fR and \fIsan_path_err_threshold\fR will be set to 1.
See the \fIsan_path_err_forget_rate\fR and \fIsan_path_err_threshold\fR
options, and "Shaky paths detection" below for more information.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B delay_wait_checks
This option is \fBdeprecated\fR, and mapped to \fIsan_path_err_recovery_time\fR.
If this is set to a value greater than 0 and no \fIsan_path_err\fR options
are set, \fIsan_path_err_recovery_time\fR will be set to the value of
\fIdelay_wait_checks\fR times \fImax_polling_interval\fR. This will give
approximately the same wait time as delay_wait_checks previously did.
Also, \fIsan_path_err_threshold\fR will be set to 1. See the
\fIsan_path_err_recovery_time\fR and \fIsan_path_err_threshold\fR
options, and "Shaky paths detection" below for more information.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B marginal_pathgroups
If set to \fIno\fR, the \fIdelay_*_checks\fR, \fImarginal_path_*\fR, and
\fIsan_path_err_*\fR options will keep marginal, or \(dqshaky\(dq, paths from
being reinstated until they have been monitored for some time. This can cause
situations where all non-marginal paths are down, and no paths are usable
until multipathd detects this and reinstates a marginal path. If the multipath
device is not configured to queue IO in this case, it can cause IO errors to
occur, even though there are marginal paths available.  However, if this
option is set to \fIyes\fR, when one of the marginal path detecting methods
determines that a path is marginal, it will be reinstated and placed in a
seperate pathgroup that will only be used after all the non-marginal pathgroups
have been tried first. This prevents the possibility of IO errors occuring
while marginal paths are still usable. After the path has been monitored
for the configured time, and is declared healthy, it will be returned to its
normal pathgroup. See "Shaky paths detection" below for more information.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B find_multipaths
This option controls whether multipath and multipathd try to create multipath
maps over non-blacklisted devices they encounter. This matters a) when a device is
encountered by \fBmultipath -u\fR during udev rule processing (a device is
blocked from further processing by higher layers - such as LVM - if and only
if it\'s considered a valid multipath device path), and b) when multipathd
detects a new device. The following values are possible:
.RS
.TP 10
.I strict
Both multipath and multipathd treat only such devices as multipath devices
which have been part of a multipath map previously, and which are therefore
listed in the \fBwwids_file\fR. Users can manually set up multipath maps using the
\fBmultipathd add map\fR command. Once set up manually, the map is
remembered in the wwids file and will be set up automatically in the future.
.TP
.I no
Multipath behaves like \fBstrict\fR. Multipathd behaves like \fBgreedy\fR.
.TP
.I yes
Both multipathd and multipath treat a device as multipath device if the
conditions for \fBstrict\fR are met, or if at least two non-blacklisted paths
with the same WWID have been detected.
.TP
.I greedy
Both multipathd and multipath treat every non-blacklisted device as multipath
device path.
.TP
.I smart
This differs from \fIfind_multipaths yes\fR only in
the way it treats new devices for which only one path has been
detected yet. When such a device is first encounted in udev rules, it is
treated as a multipath device. multipathd waits whether additional paths with
the same WWID appears. If that happens, it sets up a multipath map. If it
doesn\'t happen until a
timeout expires, or if setting up the map fails, a new uevent is triggered for
the device; at second encounter in the udev rules, the device will be treated
as non-multipath and passed on to upper layers.
\fBNote:\fR this may cause delays during device detection if
there are single-path devices which aren\'t blacklisted.
.TP
The default is: \fBstrict\fR
.RE
.
.
.TP
.B find_multipaths_timeout
Timeout, in seconds, to wait for additional paths after detecting the first
one, if \fIfind_multipaths
"smart"\fR (see above) is set. If the value is \fBpositive\fR, this timeout is used for all
unknown, non-blacklisted devices encountered. If the value is \fBnegative\fR
(recommended), it's only
applied to "known" devices that have an entry in multipath's hardware table,
either in the built-in table or in a \fIdevice\fR section; other ("unknown") devices will
use a timeout of only 1 second to avoid booting delays. The value 0 means
"use the built-in default". If \fIfind_multipath\fR has a value
other than \fIsmart\fR, this option has no effect.
.RS
.TP
The default is: \fB-10\fR (10s for known and 1s for unknown hardware)
.RE
.
.
.TP
.B uxsock_timeout
CLI receive timeout in milliseconds. For larger systems CLI commands
might timeout before the multipathd lock is released and the CLI command
can be processed. This will result in errors like
"timeout receiving packet" to be returned from CLI commands.
In these cases it is recommended to increase the CLI timeout to avoid
those issues.
.RS
.TP
The default is: \fB4000\fR
.RE
.
.
.TP
.B retrigger_tries
Sets the number of times multipathd will try to retrigger a uevent to get the
WWID.
.RS
.TP
The default is: \fB3\fR
.RE
.
.
.TP
.B retrigger_delay
Sets the amount of time, in seconds, to wait between retriggers.
.RS
.TP
The default is: \fB10\fR
.RE
.
.
.TP
.B missing_uev_wait_timeout
Controls how many seconds multipathd will wait, after a new multipath device
is created, to receive a change event from udev for the device, before
automatically enabling device reloads. Usually multipathd will delay reloads
on a device until it receives a change uevent from the initial table load.
.RS
.TP
The default is: \fB30\fR
.RE
.
.
.TP
.B skip_kpartx
If set to
.I yes
, kpartx will not automatically create partitions on the device.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B disable_changed_wwids
This option is deprecated and ignored. If the WWID of a path suddenly changes,
multipathd handles it as if it was removed and then added again.
.RE
.
.
.TP
.B remove_retries
This sets how may times multipath will retry removing a device that is in-use.
Between each attempt, multipath will sleep 1 second.
.RS
.TP
The default is: \fB0\fR
.RE
.
.
.TP
.B max_sectors_kb
Sets the max_sectors_kb device parameter on all path devices and the multipath
device to the specified value.
.RS
.TP
The default is: in \fB/sys/block/<dev>/queue/max_sectors_kb\fR
.RE
.
.
.TP
.B ghost_delay
Sets the number of seconds that multipath will wait after creating a device
with only ghost paths before marking it ready for use in systemd. This gives
the active paths time to appear before the multipath runs the hardware handler
to switch the ghost paths to active ones. Setting this to \fI0\fR or \fIno\fR
makes multipath immediately mark a device with only ghost paths as ready.
.RS
.TP
The default is: \fBno\fR
.RE
.
.
.TP
.B enable_foreign
Enables or disables foreign libraries (see section
.I FOREIGN MULTIPATH SUPPORT
below). The value is a regular expression; foreign libraries are loaded
if their name (e.g. \(dqnvme\(dq) matches the expression. By default,
no foreign libraries are enabled. Set this to \(dqnvme\(dq to enable NVMe native
multipath support, or \(dq.*\(dq to enable all foreign libraries.
.RS
.TP
The default is: \fB\(dqNONE\(dq\fR
.RE
.
.
.TP
.B recheck_wwid
If set to \fIyes\fR, when a failed path is restored, its wwid is rechecked. If
the wwid has changed, the path is removed from the current multipath device,
and re-added as a new path. Multipathd will also recheck a path's wwid if it is
manually re-added. This option only works for SCSI devices that are configured
to use the default uid_attribute, \fIID_SERIAL\fR, or sysfs for getting their
wwid.
.RS
.TP
The default is: \fBno\fR
.RE
.
.

.
.\" ----------------------------------------------------------------------------
.SH "blacklist and blacklist_exceptions sections"
.\" ----------------------------------------------------------------------------
.
The \fIblacklist\fR section is used to exclude specific devices from
the multipath topology. It is most commonly used to exclude local disks or
non-disk devices (such as LUNs for the storage array controller) from
being handled by multipath-tools.
.LP
.
.
In the \fIblacklist\fR and \fIblacklist_exceptions\fR sections, starting a
quoted value with an exclamation mark \fB"!"\fR will invert the matching
of the rest of the regular expression. For instance, \fB"!^sd[a-z]"\fR will
match all values that do not start with \fB"sd[a-z]"\fR. The exclamation mark
can be escaped \fB"\\!"\fR to match a literal \fB!\fR at the start of a
regular expression. \fBNote:\fR The exclamation mark must be inside quotes,
otherwise it will be treated as starting a comment.
.LP
.
.
The \fIblacklist_exceptions\fR section is used to revert the actions of the
\fIblacklist\fR section. This allows one to selectively include ("whitelist") devices which
would normally be excluded via the \fIblacklist\fR section. A common usage is
to blacklist "everything" using a catch-all regular expression, and create
specific blacklist_exceptions entries for those devices that should be handled
by multipath-tools.
.LP
.
.
The following keywords are recognized in both sections. The defaults are empty
unless explicitly stated.
.TP 17
.B devnode
Regular expression matching the device nodes to be excluded/included.
.RS
.PP
The default \fIblacklist\fR consists of the regular expression
\fB"!^(sd[a-z]|dasd[a-z]|nvme[0-9])"\fR. This causes all device types other
than scsi, dasd, and nvme to be excluded from multipath handling by default.
.RE
.TP
.B wwid
Regular expression for the \fIWorld Wide Identifier\fR of a device to be excluded/included.
.
.TP
.B device
Subsection for the device description. This subsection recognizes the
.B vendor
and
.B product
keywords. Both are regular expressions. For a full description of these keywords please see the
\fIdevices\fR section description.
.TP
.B property
Regular expression for an udev property. All
devices that have matching udev properties will be excluded/included.
The handling of the \fIproperty\fR keyword is special,
because devices \fBmust\fR have at least one whitelisted udev property;
otherwise they're treated as blacklisted, and the message
"\fIblacklisted, udev property missing\fR" is displayed in the logs.
.
.RS
.PP
.B Note:
The behavior of this option has changed in \fBmultipath-tools\fR 0.8.2
compared to previous versions.
Blacklisting by missing properties is only applied to devices which do have the
property specified by \fIuid_attribute\fR (e.g. \fIID_SERIAL\fR)
set. Previously, it was applied to every device, possibly causing devices to be
blacklisted because of temporary I/O error conditions.
.PP
The default \fIblacklist exception\fR is: \fB(SCSI_IDENT_|ID_WWN)\fR, causing
well-behaved SCSI devices and devices that provide a WWN (World Wide Number)
to be included, and all others to be excluded.
.RE
.TP
.B protocol
Regular expression for the protocol of a device to be excluded/included.
.RS
.PP
The protocol strings that multipath recognizes are \fIscsi:fcp\fR,
\fIscsi:spi\fR, \fIscsi:ssa\fR, \fIscsi:sbp\fR, \fIscsi:srp\fR,
\fIscsi:iscsi\fR, \fIscsi:sas\fR, \fIscsi:adt\fR, \fIscsi:ata\fR,
\fIscsi:unspec\fR, \fIccw\fR, \fIcciss\fR, \fInvme\fR, and \fIundef\fR.
The protocol that a path is using can be viewed by running
\fBmultipathd show paths format "%d %P"\fR
.RE
.LP
For every device, these 5 blacklist criteria are evaluated in the the order
"property, dev\%node, device, protocol, wwid". If a device turns out to be
blacklisted by any criterion, it's excluded from handling by multipathd, and
the later criteria aren't evaluated any more. For each
criterion, the whitelist takes precedence over the blacklist if a device
matches both.
.LP
.B
Note:
Besides the blacklist and whitelist, other configuration options such as
\fIfind_multipaths\fR have an impact on
whether or not a given device is handled by multipath-tools.
.
.
.\" ----------------------------------------------------------------------------
.SH "multipaths section"
.\" ----------------------------------------------------------------------------
.
The \fImultipaths\fR section allows setting attributes of multipath maps. The
attributes that are set via the multipaths section (see list below) take
precedence over all other configuration settings, including those from the
\fIoverrides\fR section.
.LP
The only recognized attribute for the \fImultipaths\fR section is the
\fImultipath\fR subsection. If there are multiple \fImultipath\fR subsections
matching a given WWID, the contents of these sections are merged, and settings
from later entries take precedence.
.LP
.
.
The \fImultipath\fR subsection recognizes the following attributes:
.TP 17
.B wwid
(Mandatory) World Wide Identifier. Detected multipath maps are matched agains this attribute.
Note that, unlike the \fIwwid\fR attribute in the \fIblacklist\fR section,
this is \fBnot\fR a regular expression or a substring; WWIDs must match
exactly inside the multipaths section.
.TP
.B alias
Symbolic name for the multipath map. This takes precedence over a an entry for
the same WWID in the \fIbindings_file\fR.
.LP
.
.
The following attributes are optional; if not set the default values
are taken from the \fIoverrides\fR, \fIdevices\fR, or \fIdefaults\fR
section:
.sp 1
.PD .1v
.RS
.TP 18
.B path_grouping_policy
.TP
.B path_selector
.TP
.B prio
.TP
.B prio_args
.TP
.B failback
.TP
.B rr_weight
.TP
.B no_path_retry
.TP
.B rr_min_io
.TP
.B rr_min_io_rq
.TP
.B flush_on_last_del
.TP
.B features
.TP
.B reservation_key
.TP
.B user_friendly_names
.TP
.B deferred_remove
.TP
.B san_path_err_threshold
.TP
.B san_path_err_forget_rate
.TP
.B san_path_err_recovery_time
.TP
.B marginal_path_err_sample_time
.TP
.B marginal_path_err_rate_threshold
.TP
.B marginal_path_err_recheck_gap_time
.TP
.B marginal_path_double_failed_time
.TP
.B delay_watch_checks
.TP
.B delay_wait_checks
.TP
.B skip_kpartx
.TP
.B max_sectors_kb
.TP
.B ghost_delay
.RE
.PD
.LP
.
.
.\" ----------------------------------------------------------------------------
.SH "devices section"
.\" ----------------------------------------------------------------------------
.
\fImultipath-tools\fR have a built-in device table with reasonable defaults
for more than 100 known multipath-capable storage devices. The devices section
can be used to override these settings. If there are multiple matches for a
given device, the attributes of all matching entries are applied to it.
If an attribute is specified in several matching device subsections,
later entries take precedence. Thus, entries in files under \fIconfig_dir\fR (in
reverse alphabetical order) have the highest precedence, followed by entries
in \fImultipath.conf\fR; the built-in hardware table has the lowest
precedence. Inside a configuration file, later entries have higher precedence
than earlier ones.
.LP
The only recognized attribute for the \fIdevices\fR section is the \fIdevice\fR
subsection. Devices detected in the system are matched against the device entries
using the \fBvendor\fR, \fBproduct\fR, and \fBrevision\fR fields, which are
all POSIX Extended regular expressions (see \fBregex\fR(7)).
.LP
The vendor, product, and revision fields that multipath or multipathd detect for
devices in a system depend on the device type. For SCSI devices, they correspond to the
respective fields of the SCSI INQUIRY page. In general, the command '\fImultipathd show
paths format "%d %s"\fR' command can be used to see the detected properties
for all devices in the system.
.LP
.
The \fIdevice\fR subsection recognizes the following attributes:
.TP 17
.B vendor
(Mandatory) Regular expression to match the vendor name.
.TP
.B product
(Mandatory) Regular expression to match the product name.
.TP
.B revision
Regular expression to match the product revision. If not specified, any
revision matches.
.TP
.B product_blacklist
Products with the given \fBvendor\fR matching this string are
blacklisted. This is equivalent to a \fBdevice\fR entry in the \fIblacklist\fR
section with the \fIvendor\fR attribute set to this entry's \fIvendor\fR, and
the \fIproduct\fR attribute set to the value of \fIproduct_blacklist\fR.
.TP
.B alias_prefix
The user_friendly_names prefix to use for this
device type, instead of the default "mpath".
.TP
.B vpd_vendor
The vendor specific vpd page information, using the vpd page abbreviation.
The vpd page abbreviation can be found by running \fIsg_vpd -e\fR. multipathd
will use this information to gather device specific information that can be
displayed with the \fI%g\fR wilcard for the \fImultipathd show maps format\fR
and \fImultipathd show paths format\fR commands. Currently only the
\fBhp3par\fR vpd page is supported.
.TP
.B hardware_handler
The hardware handler to use for this device type.
The following hardware handler are implemented:
.RS
.TP 12
.I 1 emc
(Hardware-dependent)
Hardware handler for DGC class arrays as CLARiiON CX/AX and EMC VNX and Unity
families.
.TP
.I 1 rdac
(Hardware-dependent)
Hardware handler for LSI/Engenio/NetApp RDAC class as NetApp SANtricity E/EF
Series, and OEM arrays from IBM DELL SGI STK and SUN.
.TP
.I 1 hp_sw
(Hardware-dependent)
Hardware handler for HP/COMPAQ/DEC HSG80 and MSA/HSV arrays with
Active/Standby mode exclusively.
.TP
.I 1 alua
(Hardware-dependent)
Hardware handler for SCSI-3 ALUA compatible arrays.
.TP
.I 1 ana
(Hardware-dependent)
Hardware handler for NVMe ANA compatible arrays.
.PP
The default is: \fB<unset>\fR
.PP
\fBImportant Note:\fR Linux kernels 4.3 and newer automatically attach a device
handler to known devices (which includes all devices supporting SCSI-3 ALUA)
and disallow changing the handler
afterwards. Setting \fBhardware_handler\fR for such devices on these kernels
has no effect.
.RE
.
.
.LP
The following attributes are optional; if not set the default values
are taken from the \fIdefaults\fR
section:
.sp 1
.PD .1v
.RS
.TP 18
.B path_grouping_policy
.TP
.B uid_attribute
.TP
.B getuid_callout
.TP
.B path_selector
.TP
.B path_checker
.TP
.B prio
.TP
.B prio_args
.TP
.B features
.TP
.B failback
.TP
.B rr_weight
.TP
.B no_path_retry
.TP
.B rr_min_io
.TP
.B rr_min_io_rq
.TP
.B fast_io_fail_tmo
.TP
.B dev_loss_tmo
.TP
.B flush_on_last_del
.TP
.B user_friendly_names
.TP
.B retain_attached_hw_handler
.TP
.B detect_prio
.TP
.B detect_checker
.TP
.B deferred_remove
.TP
.B san_path_err_threshold
.TP
.B san_path_err_forget_rate
.TP
.B san_path_err_recovery_time
.TP
.B marginal_path_err_sample_time
.TP
.B marginal_path_err_rate_threshold
.TP
.B marginal_path_err_recheck_gap_time
.TP
.B marginal_path_double_failed_time
.TP
.B delay_watch_checks
.TP
.B delay_wait_checks
.TP
.B skip_kpartx
.TP
.B max_sectors_kb
.TP
.B ghost_delay
.TP
.B all_tg_pt
.RE
.PD
.LP
.
.
.\" ----------------------------------------------------------------------------
.SH "overrides section"
.\" ----------------------------------------------------------------------------
.
The overrides section recognizes the following optional attributes; if not set
the values are taken from the \fIdevices\fR or \fIdefaults\fR sections:
.sp 1
.PD .1v
.RS
.TP 18
.B path_grouping_policy
.TP
.B uid_attribute
.TP
.B getuid_callout
.TP
.B path_selector
.TP
.B path_checker
.TP
.B alias_prefix
.TP
.B features
.TP
.B prio
.TP
.B prio_args
.TP
.B failback
.TP
.B rr_weight
.TP
.B no_path_retry
.TP
.B rr_min_io
.TP
.B rr_min_io_rq
.TP
.B flush_on_last_del
.TP
.B fast_io_fail_tmo
.TP
.B dev_loss_tmo
.TP
.B user_friendly_names
.TP
.B retain_attached_hw_handler
.TP
.B detect_prio
.TP
.B detect_checker
.TP
.B deferred_remove
.TP
.B san_path_err_threshold
.TP
.B san_path_err_forget_rate
.TP
.B san_path_err_recovery_time
.TP
.B marginal_path_err_sample_time
.TP
.B marginal_path_err_rate_threshold
.TP
.B marginal_path_err_recheck_gap_time
.TP
.B marginal_path_double_failed_time
.TP
.B delay_watch_checks
.TP
.B delay_wait_checks
.TP
.B skip_kpartx
.TP
.B max_sectors_kb
.TP
.B ghost_delay
.TP
.B all_tg_pt
.RE
.PD
.LP
.
.
.\" ----------------------------------------------------------------------------
.SH "WWID generation"
.\" ----------------------------------------------------------------------------
.
Multipath uses a \fIWorld Wide Identification\fR (WWID) to determine
which paths belong to the same device. Each path presenting the same
WWID is assumed to point to the same device.
.LP
The WWID is generated by four methods (in the order of preference):
.TP 17
.B uid_attrs
The WWID is derived from udev attributes by matching the device node name; cf
\fIuid_attrs\fR above.
.TP
.B getuid_callout
Use the specified external program; cf \fIgetuid_callout\fR above.
Care should be taken when using this method; the external program
needs to be loaded from disk for execution, which might lead to
deadlock situations in an all-paths-down scenario.
.TP
.B uid_attribute
Use the value of the specified udev attribute; cf \fIuid_attribute\fR
above. This method is preferred to \fIgetuid_callout\fR as multipath
does not need to call any external programs here. However, under
certain circumstances udev might not be able to generate the requested
variable.
.TP
.B sysfs
Try to determine the WWID from sysfs attributes.
For SCSI devices, this means reading the Vital Product Data (VPD) page
\(dqDevice Identification\(dq (0x83).
.PP
The default settings (using udev and \fBuid_attribute\fR configured from
the built-in hardware table) should work fine
in most scenarios. Users who want to enable uevent merging must set
\fBuid_attrs\fR.
.
.
.\" ----------------------------------------------------------------------------
.SH "Shaky paths detection"
.\" ----------------------------------------------------------------------------
.
A common problem in SAN setups is the occurence of intermittent errors: a
path is unreachable, then reachable again for a short time, disappears again,
and so forth. This happens typically on unstable interconnects. It is
undesirable to switch pathgroups unnecessarily on such frequent, unreliable
events. \fImultipathd\fR supports three different methods for detecting this
situation and dealing with it. All methods share the same basic mode of
operation: If a path is found to be \(dqshaky\(dq or \(dqflipping\(dq,
and appears to be in healthy status, it is not reinstated (put back to use)
immediately. Instead, it is placed in the \(dqdelayed\(dq state and watched
for some time, and only reinstated if the healthy state appears to be stable.
If the \fImarginal_pathgroups\fR option is set, the path will reinstated
immediately, but placed in a special pathgroup for marginal paths. Marginal
pathgroups will not be used until all other pathgroups have been tried. At the
time when the path would normally be reinstated, it will be returned to its
normal pathgroup. The logic of determining \(dqshaky\(dq condition, as well as
the logic when to reinstate, differs between the three methods.
.TP 8
.B \(dqdelay_checks\(dq failure tracking
This method is \fBdeprecated\fR and mapped to the \(dqsan_path_err\(dq method.
See the \fIdelay_watch_checks\fR and \fIdelay_wait_checks\fR options above
for more information.

.TP
.B \(dqmarginal_path\(dq failure tracking
If a second failure event (good->bad transition) occurs within
\fImarginal_path_double_failed_time\fR seconds after a failure, high-frequency
monitoring is started for the affected path: I/O is sent at a rate of 10 per
second. This is done for \fImarginal_path_err_sample_time\fR seconds. During
this period, the path is not reinstated. If the
rate of errors remains below \fImarginal_path_err_rate_threshold\fR during the
monitoring period, the path is reinstated. Otherwise, it
is kept in failed state for \fImarginal_path_err_recheck_gap_time\fR, and
after that, it is monitored again. For this method, time intervals are measured
in seconds.
.TP
.B \(dqsan_path_err\(dq failure tracking
multipathd counts path failures for each path. Once the number of failures
exceeds the value given by \fIsan_path_err_threshold\fR, the path is not
reinstated for \fIsan_path_err_recovery_time\fR seconds. While counting
failures, multipathd \(dqforgets\(dq one past failure every
\(dqsan_path_err_forget_rate\(dq ticks; thus if errors don't occur more
often then once in the forget rate interval, the failure count doesn't
increase and the threshold is never reached. Ticks are the time between
path checks by multipathd, which is variable and controlled by the
\fIpolling_interval\fR and \fImax_polling_interval\fR parameters.
.
.RS 8
.LP
This method is \fBdeprecated\fR in favor of the \(dqmarginal_path\(dq failure
tracking method, and only offered for backward compatibility.
.
.RE
.LP
See the documentation
of the individual options above for details.
It is \fBstrongly discouraged\fR to use more than one of these methods for any
given multipath map, because the two concurrent methods may interact in
unpredictable ways. If the \(dqmarginal_path\(dq method is active, the
\(dqsan_path_err\(dq parameters are implicitly set to 0.
.
.
.\" ----------------------------------------------------------------------------
.SH "FOREIGN MULTIPATH SUPPORT"
.\" ----------------------------------------------------------------------------
.
multipath and multipathd can load \(dqforeign\(dq libraries to add
support for other multipathing technologies besides the Linux device mapper.
Currently this support is limited to printing detected information about
multipath setup. In topology output, the names of foreign maps are prefixed by
the foreign library name in square brackets, as in this example:
.
.P
.EX
# multipath -ll
uuid.fedcba98-3579-4567-8765-123456789abc [nvme]:nvme4n9 NVMe,Some NVMe controller,FFFFFFFF
size=167772160 features='n/a' hwhandler='ANA' wp=rw
|-+- policy='n/a' prio=50 status=optimized
| `- 4:38:1    nvme4c38n1 0:0     n/a   optimized    live
`-+- policy='n/a' prio=50 status=optimized
  `- 4:39:1    nvme4c39n1 0:0     n/a   optimized    live
.EE
.
.P
The \(dqnvme\(dq foreign library provides support for NVMe native multipathing
in the kernel. It is part of the standard multipath package.
.
.\" ----------------------------------------------------------------------------
.SH "KNOWN ISSUES"
.\" ----------------------------------------------------------------------------
.
The usage of \fIqueue_if_no_path\fR option can lead to \fID state\fR
processes being hung and not killable in situations where all the paths to the
LUN go offline. It is advisable to use the \fIno_path_retry\fR option instead.
.P
The use of \fIqueue_if_no_path\fR or \fIno_path_retry\fR might lead to a
deadlock if the \fIdev_loss_tmo\fR setting results in a device being removed
while I/O is still queued. The multipath daemon will update the \fIdev_loss_tmo\fR
setting accordingly to avoid this deadlock. Hence if both values are
specified the order of precedence is \fIno_path_retry, queue_if_no_path, dev_loss_tmo\fR.
.
.
.\" ----------------------------------------------------------------------------
.SH "SEE ALSO"
.\" ----------------------------------------------------------------------------
.
.BR udev (8),
.BR dmsetup (8),
.BR multipath (8),
.BR multipathd (8).
.
.
.\" ----------------------------------------------------------------------------
.SH AUTHORS
.\" ----------------------------------------------------------------------------
.
\fImultipath-tools\fR was developed by Christophe Varoqui, <christophe.varoqui@opensvc.com>
and others.
.\" EOF
